1. Technical Field
The present invention relates generally to a semiconductor integrated circuit, and more particularly, to an anti-fuse circuit.
2. Related Art
When, any one failed unit cell among numerous unit cells of is a semiconductor memory apparatus is detected, during a fabrication process for the semiconductor memory apparatus, the semiconductor memory apparatus may not function to retain memory, and thus is discarded as a defective product. However, it is inefficient to discard the entire semiconductor memory apparatus and designate it as a defective product even though the defects have only occurred in certain unit cells thereof. Therefore, the semiconductor memory apparatus may be restored by replacing the failed unit cells with redundancy cells prepared therein, which makes it possible to improve the yield of semiconductor memory apparatuses.
A repair operation using redundancy cells may be performed at a wafer level and a package level. At the wafer level, a fuse is used to perform a repair operation. For example, the repair operation using a fuse may include the method of cutting a fuse existing in a line connected to a row or column having a failed cell by passing an over current, a method of burning a fuse using laser beams, a method of connecting junctions using laser beams, and a method of programming a fuse through EPROM, in order to replace failed cells with redundancy cells.
On the other hand, the repair operation using a fuse cannot be performed at the package level. Therefore, an anti-fuse may be adopted to perform a repair operation. The anti-fuse is a resistive fuse element having an electrical characteristic opposite the fuse. In general, the anti-fuse may be formed of a thin dielectric material such as a complex in which a dielectric such as SiO2, silicon nitride, tantalum oxide, or ONO (silicon dioxide-silicon nitride-silicon dioxide) is interposed between two conductors. The anti-fuse is electrically open in a normal state. However, when a high voltage is applied to destroy the dielectric between the conductors, the anti-fuse is shorted. That is, when a failed cell is to be replaced at the package level, a programming operation of applying a high voltage to an anti-fuse circuit is performed. After the programming operation, the anti-fuse is shorted to replace the failed cell with a redundancy cell.
FIG. 1 is a conventional anti-fuse circuit provided in a semiconductor apparatus.
In order to perform a repair operation on a memory cell, an activated rupture signal RUP is applied to the anti-fuse circuit to program an anti-fuse corresponding to the memory cell. The anti-fuse is electrically open in a normal state. However, when a high voltage (i.e., VHIGH) is applied to destroy a dielectric of the anti-fuse, the anti-fuse is shorted. FIG. 1 illustrates a gate oxide anti-fuse which looses the property of an NMOS transistor and has the property of a conductor when receiving a high voltage through a gate terminal thereof. In addition, however, various types of anti-fuses may be used.
The conventional anti-fuse circuit includes a fuse unit 10, a reset unit 40, and an output unit 50.
The fuse unit 10 may include an inverter IV1, a PMOS transistor P1, a pass gate PG1, an anti-fuse AF1, the reset unit 40 may include a PMOS transistor P2, and the output unit 50 may is include an inverter IV2.
The reset unit 40 is configured to receive a power-up signal PWR and reset an output node ND to an external voltage level VDD, during initial power up. Therefore, before a programming operation is performed, a deactivated fuse signal FUSE is generated through the output unit 50.
On the other hand, when the rupture signal RUP is applied, the anti-fuse AF1 of the fuse unit 10 is programmed, and the pass gate PG1 is enabled to lower the voltage level of the output node ND to a ground voltage level VSS. Therefore, after the programming operation, the activated fuse signal FUSE is generated through the output unit 50.
That is, the conventional anti-fuse circuit generates the activated fuse signal by programming the anti-fuse, thereby replacing the corresponding memory cell with a redundancy cell.
In the conventional anti-fuse circuit, however, the anti-fuse sensitively reacts with external environments. Therefore, although a programming operation was not performed, the anti-fuse may be destroyed. Furthermore, since a programming operation is performed at the package level, the anti-fuse resistance after the programming operation may deviate from a sensing range. In this case, a false fuse signal may be generated to cause a malfunction of the entire semiconductor apparatus.